1. Field of the Invention
The present invention relates to an ink, an ink-jet recording method employing the ink, and an apparatus employing the ink. More particularly, the present invention relates to a recording liquid which gives high density and water resistance of printed letters on non-coated paper such as wood-free paper, paper for copying, bond paper, paper for reporting, and the like, and which gives improved indoor discoloration of an image recorded on coated paper having an image-receiving layer thereon composed of a binder and a pigment. The present invention also relates to an ink-jet recording method, an ink-jet recording unit, an ink-jet recording apparatus, and an ink cartridge.
2. Related Background Art
Heretofore, aqueous inks having a water-soluble dye dissolved in an aqueous medium have been used for ink-jet recording. The inks for such a use are required to have the properties as below:
(1) giving sufficient density of images, PA0 (2) having satisfactory drying property on recording mediums, PA0 (3) causing little feathering or running of images, PA0 (4) causing no flowing-out of the recorded images when brought into contact with water, alcohol, or the like, or allowing satisfactory decipherment even when some flowing out occurs (water-resistance), PA0 (5) giving high light-fastness of recorded images, PA0 (6) causing no clogging of a tip of a pen or a nozzle, PA0 (7) causing no inconvenience in printed images such as blurring and scratching in continuous recording or at the re-start of recording after a long term of intermission of the recording (ejection stability), PA0 (8) being stable during storage, PA0 (9) causing no problem on contact with a constituting member of a recording means on use, PA0 (10) giving no hazard to an operator, and so forth. Furthermore, in an ink-jet recording system, utilizing thermal energy, the property below is required in addition to the above requirements: PA0 (11) having high heat resistance, and giving no adverse influence to a thermal energy-generating means.
As a specific example of the dye, C.I. Food Black 2 is mainly used in ink-jet recording for both mono-color and full-color images (see Japanese Patent Application Laid-open No. 59-93766, and No. 59-93768).
An ink using C.I. Food Black 2 is satisfactory in density of recorded images, but still involves problems on light-fastness and water-resistance of recorded images: the black color turns brown on prolonged light exposure or on posting-up of printed matters in proximity to a copying machine, resulting in remarkable deterioration of the image quality, and difficulty in decipherment in test of water-spilling.
An ink is disclosed which has ejection stability, water resistance of images, and other properties improved by introducing at least one specific structural unit into a dye structure in Japanese Patent Application Laid-open No. 1-135880. Further, a recording liquid of black color is disclosed, in Japanese Patent Application Laid-open No. 1-193375, which has high affinity to recording media, and is superior in fixability and water-resistance, giving satisfactory quality of printed letters on an ordinary paper. Furthermore, a recording liquid is disclosed which is improved in ejection stability, and light fastness of images in Japanese Patent Publication No. 62-010274.
The ink is required firstly to have suitability for an employed recording system, and secondly is required to give satisfactory properties of printed matters such as quality and fastness of the images. However, it is considerably difficult to satisfy simultaneously all of the aforementioned various requirements on performances, as understood from the prior art disclosures cited above.
The quality of the printed letters mostly depends on a liquid medium of the ink, although it depends secondarily on properties of the dye itself.
The fastness of the printed matter is directly influenced by the dye properties. In particular, light-fastness is the most important of the fastnesses, and improvement of the light-fastness has been tried as described above.
Another problem, which has not been noticed but has come to be noticed as a consequence of technical progress, is discoloration or color change. The discoloration is especially serious in black ink which is used in a large quantity. In full color images, the image quality deteriorates rapidly by the discoloration.
The discoloration proceeds indoors also without direct sunlight illumination. The discoloration further depends on the kind of a recording medium for forming images thereon, being remarkable on paper containing silica or the like as a pigment. The widely used C.I. Food Black 2 is not free from this problem.
Dyes having satisfactory light-fastness have been sought in order to cancel the disadvantage of C.I. Food Black 2. Consequently, dyes are found which are satisfactory for use on ordinary paper. However, the ink causing less problems on ordinary paper discolors significantly on coated paper which has an ink-receiving layer formed on a substrate and containing a pigment and a binder for the purpose of improving image quality such as color-developing property of the dyes, sharpness, and resolution. Thus the problem is not solved by merely employing a light-fast dye.